The invention relates generally to photocopiers employing liquid toner developer, and particularly to apparatus for removing excess liquid developer from a photosensitive drum surface before transfer of the image to a copy material.
In a photocopier employing a rotating photosensitive drum surface, the drum surface is electrically charged and then exposed to an original light pattern to form a latent electrostatic image on the surface. The latent image is developed, for example by contacting a liquid developer to the image, and the developed image is transferred onto copy material by a transfer process. The drum is thereafter cleaned and used again.
In photocopiers employing liquid toner development, it is necessary prior to the transfer step to remove excess liquid developer remaining on the drum after development. The development process is not precise, and excess developer remaining on the drum surface can cause a blurry or fuzzy image on the transfer material and can excessively wet the transfer material so that drying would either take longer or be incomplete.
Among the devices used in the past to remove excess liquid from a wet surface have been rollers of one form or another. For example, in the printing and paper industry, it was common to rest a roller directly on the wet surface to remove excess liquid. (See for example U.S. Pat. No. 3,245,377, to Gettel). In those applications wherein the roller could not be placed directly upon the surface, various methods and apparatus for maintaining the roller spaced above the surface were employed. For example, the roller axis or shaft could be fixed to the apparatus frame (for example Australian Pat. No. 269855), or the roller could be supported by roller bearings which ride on, and are driven by, the surface being controlled. Each of these apparatus configurations was available prior to the introduction of the first plain paper liquid copiers, and apparatus employing the roller bearing method and apparatus described earlier were adopted almost simultaneously by at least two competing manufacturers for their commercial photocopiers. The manufacturers merely differed with respect to the direction of rotation of the operational roller, the different rotation directions having also been considered and disclosed previously in connection with related operating systems.
In each apparatus employing roller bearings to space the roller from the drum surface, the roller rotates with respect to the roller bearings. It is therefore imperative to provide bushings, bearings, or the equivalent structure between the two differentially rotating parts. The adjustment, lubrication, and most importantly, the sealing of these roller bearings require careful attention, consideration, and control, and effectively increase the cost of the apparatus. Further, the commercial apparatus employing the roller bearing systems often employed hardened drum edges, for example, anodized aluminum, to further reduce wear from the rolling friction of the roller bearings on the drum.
In U.S. application Ser. No. 40,901, to Davis, filed May 21, 1979 and assigned to the same Assignee as the present application, there was disclosed a metering roll with distance control portions rigidly secured to its ends. The distance control portions had exterior dimensions selected to keep the central metering portion of the roll a fixed distance from the central drum surface. The surfaces of the distance control portions were in sliding frictional contact only with the surface of the drum against which they were biased.
That metering roll, however, still required a careful axial arrangement of multi-level surfaces to provide the required gap between the metering portion of the roll and the drum surface. It required careful dimensional control of the outer surface of the distance control portions, and if they were separately made, as is likely, careful coaxial alignment of the distance control portion and the metering portion when they are secured together.
Accordingly, it is an object of this invention to provide a reliable, relatively inexpensive metering apparatus that does not require the precise coaxial alignment of earlier metering rolls. A further object of the invention is to provide a metering apparatus that is easier and less expensive to manufacture, that has low wear characteristics, that has a long lifetime, and that is substantially unaffected by the liquid toner developer solutions.